A computer database system may be divided into partitions that are separately stored and accessed. The partitions may be divided into data fragments including a plurality of records or rowsets that may be stored on separate network nodes, allowing multiple queries for different records to be processed in parallel. To further improve reliability, the data fragments may be cloned. By maintaining multiple clones per data fragment, in the event that one clone becomes unavailable or becomes potentially or actually outdated as a result of a media failure or a host computer failure, one or more remaining clones may be used in order to preserve access to the data fragments.
While it may be advantageous to permit data to be read from or written to another clone when one clone is unavailable, this may result in different data being stored in clones that are intended to store the same data. It is also possible that, while clones of the same data fragment may store the same data, because of the unavailability of a clone, it may not be known whether a previously unavailable clone stores current data.